1. Field of the Invention
The present invention relates to a hydrogen plasma downstream treatment equipment and a hydrogen plasma downstream treatment method and, more particularly, a so-called dry process for cleaning a surface of a semiconductor layer by placing a semiconductor layer in the downstream of the plasmanized reaction gas region and an equipment for embodying the dry process.
2. Description of the Prior Art
In recent years, influences of a native oxide film formed on a surface of the silicon substrate upon electric characteristics of film quality of an upper film formed on the natural oxide film and electric characteristics at a boundary between respective layers upon growth of metal, silicon, etc. have not been able to be ignored in production of a semiconductor device, in particular, a large scale integrated circuit using a silicon substrate. Therefore, it is needed more and more to remove the native oxide film quickly and at low temperature.
As means for achieving such necessity at best, an NF.sub.3 -added hydrogen and water-vapor plasma downstream treatment has been known. In such NF.sub.3 -added hydrogen and water-vapor plasma downstream treatment, the native oxide film formed on the surface of the silicon substrate is removed by means of NF.sub.3 -added gas which can be obtained by plasmanizing a gas mixture of hydrogen and water-vapor and then adding unplasmanized NF.sub.3 in the downstream of such gas flow, so that bonds of atoms on the surface are terminated.
J. Kikuchi, M. Iga, H. Ogawa, S. Fujiwara, and H. Yano, "Native Oxide Removal on Si Surface by NF.sub.3 -added Hydrogen and Water-vapor Plasma Downstream Treatment", Jpn. J. Appl. Phys., 33, 2207-2211 (1994).
According to this technique, generation of fluorine atoms due to dissociation of NF.sub.3 caused by collision between NF.sub.3 and high energy particles such as electrons, cations, photons, etc. in the plasma can be avoided by adding NF.sub.3 in the downstream of the plasmanized gas mixture of hydrogen and water-vapor. For this reason, there is no fluorine on the surface of the substrate which has been subjected to such treatment, and also there is no possibility that the fluorine atoms etch an inner wall of the vacuum chamber such as quartz to thus produce particles. This technique has been set forth in, for example, an article of J. Kikuchi, M. Nagasaka, S. Fujimura, H. Yano, and Y. Horiike, "Cleaning of Silicon Surface by NF.sub.3 -added Hydrogen and Water-vapor Plasma Downstream Treatment", Jpn. J. Appl. Phys., 35, 1022-1026 (1996).
Prior to such report about to the treatment which is executed by adding NF.sub.3 in the downstream of the plasmanized gas mixture of hydrogen and water-vapor, the NF.sub.3 +NH.sub.3 plasma downflow treatment and the NF.sub.3 +H.sub.2 plasma downflow treatment to execute etching of the silicon oxide film have been reported in an article described in the following, but there has been no difference in advantage between the above NF.sub.3 -added hydrogen and water-vapor plasma downstream treatment and the NF.sub.3 +NH.sub.3 plasma downflow treatment or the NF.sub.3 +H.sub.2 plasma downflow treatment. Where the "downstream treatment" and the "downflow treatment" have almost the same meaning, as shown in next document. NF.sub.3 +NH.sub.3 : H. Nishino, N. Hayasaka, H. Ito, T. Arikado, and H. Okano, Proc. Symp. Dry Process, 1989, Tokyo (The Institute of Electrical Engineers of Japan, Tokyo, 1989) p.90, NF.sub.3 +H.sub.2 : T. Kusuki, H. Kawakami, H. Sakaue, and Y. Horiike, Ext. Abstr. Electrochem. Soc., Hawaii (1993), p.375.
The treatment which is executed by adding NF.sub.3 in the downstream of the plasmanized gas mixture of hydrogen and water-vapor is rather effective as the native oxide film removing method. However, a region to cause sufficient reaction between NF.sub.3 and hydrogen atoms is required so as to produce HF, NH.sub.3 F, etc. and thus the treatment equipment is increased in size.
The NF.sub.3 +NH.sub.3 plasma downflow treatment and the NF.sub.3 +H.sub.2 plasma downflow treatment have had such an advantage that the treatment equipment is not increased in size, but various problems such that a large quantity of deposits (particles) are produced, fluorine still remain on the surface of the substrate from which the native oxide film is removed, etc. have been reported.
However, both the NF.sub.3 +NH.sub.3 plasma downflow treatment and the NF.sub.3 +H.sub.2 plasma downflow treatment are the plasma downflow treatment in which two kind of gases are mixed simply and therefore implementation of the treatment is relatively simple. In particular, the treatment using NF.sub.3 +H.sub.2 has been commonly employed in mass production steps of the semiconductor device, and are excellent in easy handling together with safety aspect. Therefore, if the problems about to the particles and fluorine can be reduced, the treatment using NF.sub.3 +H.sub.2 is of utility value according to individual applications since the native oxide film can be removed at low cost rather than the treatment which is executed by adding NF.sub.3 in the downstream of the plasmanized gas mixture of hydrogen and water-vapor.